Due to the remarkable technological development in wired data communications, various networks based on the Internet protocol (IP) have become prevalent so as to provide various communication services such as high-speed and low-cost communication services. In contrast, IP radio communications using user equipments (UE) such as cellular phones and portable information terminals in mobile communications have not become prevalent compared to wired data communications.
The recent mobile communication technology has been developed to facilitate small-scale radio base stations, which enable communications in the femtocell ranging from several meters to several tens of meters, in homes and small offices (e.g. SOHO: Small Office Home Office), thus providing users with high-speed and low-cost communications. Small-scale radio base stations are devices that provide user equipments with mobile communications but that have limited capabilities of communications ranging from several meters to several tens of meters due to low radio output powers. Small-scale radio base stations are reduced in communication ranges and in the number of user equipments connected thereto so as to allocate relatively broad bands to user equipments, thus providing high-speed and low-cost communications.
Small-scale radio base stations are connected to core networks (CN) (which are wired communication networks) via the Internet or telephone lines such as digital subscriber lines (DSL).
The femtocell using small-scale radio base stations is advantageous for subscribers and mobile communication operators. Conventionally, a large number of radio base stations covering numerous user equipments are required to achieve wide communication areas, whereas since radio base stations are high-cost facilities, they impose heavy economic burdens on mobile communication operators. In contrast, small-scale radio base stations are low-cost devices which can be easily sold or rent on the market, thus reducing economic burdens on mobile communication operators. In addition, small-scale radio base stations which are set up by subscribers can be precisely installed in requested locations in mobile communications.
The 3GPP has developed the Home Node-B (H NB) and Home Evolved Node-B (H(e) NB) providing communications to the Closed Subscriber Group (CSG), which is disclosed in Non-Patent Document 1.    Non-Patent Document 1: 3GPP TS 22.011 V8.3.0 (2008-03), Technical Specification 3rd Generation Partnership Project; Technical Specification Group Services and System Aspects; Service Accessibility (Release 8)
Since small-scale radio base stations adapted to small offices and home offices (SOHO) are designed to use radio communications, they may slightly extend communication ranges in the surrounding area of SOHO. Small-scale radio base stations extending communication ranges outside the SOHO are likely exploited by unauthenticated persons without being detected by subscribers and operators.
For the purposes of extending communication ranges, providing mobile communications to visitors (who visit the SOHO), and providing mobile communications to requested user equipments, small-scale radio base stations may be frequently set to the open-access mode allowing subscribers of mobile communication networks to connect thereto; hence, they are vulnerable to unauthenticated exploitation.
When unauthenticated persons (e.g. intruders/attackers who exploit small-scale radio base stations by use of communication ranges extended in the periphery of or outside of the SOHO) dominate relatively large communication bands, authenticated subscribers and/or trusted subscribers (who are permitted to use small-scale radio base stations) may not secure adequate communication ranges.
It is difficult to specify unauthenticated persons who exploit small-scale radio base stations so as to connect to core networks, so that they may deliver jamming attacks on operators' services of mobile communication networks. In addition, unauthenticated persons may control user equipments connected to small-scale radio base stations so as to further enlarge communication ranges, thus fostering unauthenticated exploitation.
Several countermeasures can be taken against unauthenticated exploitation. For example, subscribers voluntarily designate closed subscriber groups including specific subscribers who are permitted to use small-scale radio base stations, thus preventing unauthenticated exploitation. However, there still remains a possibility that subscribers of closed subscriber groups and/or other persons who steal subscribers' user equipments may unauthentically exploit small-scale radio base stations so as to increase traffic in communications; this makes it difficult for authenticated subscribers to secure adequate communication bands.